This invention relates to a method of making sulfate pulp. More particularly, the invention relates to a delignification by delignifying in batch digesters.
In making sulfate pulp for bleaching, at present the cooking is interrupted at kappa number 30-35. A continued delignification in the charge to the kappa number range 20-25 could be of interest as an alternative, for example, to oxygen bleaching, for reducing the discharge. An extension of the sulfate cooking, however, involves certain problems, expecially in respect of pulp yield and pulp viscosity.